The present invention relates to a new and distinctive squash inbred line, designated inbred 833. There are numerous steps in the development of any novel, desirable plant germplasm. Plant breeding begins with the analysis and definition of problems and weaknesses of the current germplasm, the establishment of program goals, and the definition of specific breeding objectives. The next step is selection of germplasm that possess the traits to meet the program goals. The goal is to combine in a single variety or hybrid an improved combination of desirable traits from the parental germplasm. These important traits may include higher yield, field performance, fruit and agronomic quality such as smoothness, moist texture, color, shape and size, flesh color or texture, resistance to diseases and insects, tolerance to drought and heat, plant habit and size, easier harvest ability, less need for fertilizers.
Practically speaking, all cultivated forms of squash belong to genus Cucurbita that is grown for its edible fruit. As a crop, squash, whether summer or winter squash, are grown commercially wherever environmental conditions permit the production of an economically viable yield. Both are harvested by hand. Squash usually develop a running vine on the soil but today's summer squash have been developed in the form of a short compact bush, making them easier to grow in smaller spaces. On healthy winter squash plants, there is a canopy of large, reniform and serrated leaves, which may be without lobes or with very deep ones. Fruit flesh can be of various shade of yellow, or even from white to orange. The fruits may have a soft or a hard shell with colors from dull to bright. Summer squash show a great variety of shape, cylindrical, long, flat, etc., with sizes from small to large and colors from uniform to variegated. The flesh can range from white to yellow and, contrary to the winter squash that has a flesh finely grained, bear coarse grains. In the United States, the principal fresh market squash growing regions are California, Florida and Georgia which produce approximately 30,000 acres out of a total annual acreage of more than 57,000 acres (USDA, 2000). Fresh squash are available in the United States year-round although the greatest supply is from June through October. Summer squash are consumed immature as table vegetables and winter squash are used when ripe as table vegetable or in pie.
Cucurbita pepo is a member of the family Cucurbitaceae. The Cucurbitaceae is a family of about 90 genera and 700 to 760 species, mostly of the tropics. The family includes pumpkins, squash, gourds, watermelon, loofah and several weeds. The genus cucurbita, to which the squash belongs, includes four major species, pepo, argyrosperma, moschata, and maxima, one minor species, ficifolia and some wild ones. Cross-pollination is near complete among the different cucurbita species. This offers breeders a great potential for inter-specific crosses using conventional breeding procedures. Cucurbita pepo L. refers to what is commonly known as the summer squash such as scallop, zucchini, straightneck and crookneck types and winter squash such as acorn and pumpkin. The term squash itself has a rather large meaning. Generally, it can be said that if the plant produce fruits to be harvested in an immature stage, they are called summer squash, and if the fruits are to be harvested at maturity, they are called winter squash.
Squash is a simple diploid species with twelve pairs of highly differentiated chromosomes. The plants are monoecious, with separate female and male flowers on the same plant. Usually the first four or five flowers produced are male, then the next eight or so are female, followed by a few more male and female flowers. Male flowers have 3-5 erect stamens bunched within the corolla of 5 fused petals. Female flowers have 3 spreading stigma lobes and an immature fruit (ovary) below the perianth. The spiny, sticky pollen requires insects for pollination. The primary pollinators are bees, particularly honey bees. Pollination generally occurs in the morning after the flowers open.
Choice of breeding or selection methods depends on the mode of plant reproduction, the heritability of the trait(s) being improved, and the type of cultivar used commercially (e.g., F1 hybrid cultivar, pureline cultivar, etc.). For highly heritable traits, a choice of superior individual plants evaluated at a single location will be effective, whereas for traits with low heritability, selection should be based on mean values obtained from replicated evaluations of families of related plants. Popular selection methods commonly include pedigree selection, modified pedigree selection, mass selection, and recurrent selection.
The complexity of inheritance influences choice of the breeding method. Backcross breeding is used to transfer one or a few favorable genes for a highly heritable trait into a desirable cultivar. This approach has been used extensively for breeding disease-resistant cultivars. Various recurrent selection techniques are used to improve quantitatively inherited traits controlled by numerous genes. The use of recurrent selection in self-pollinating crops depends on the ease of pollination, the frequency of successful hybrids from each pollination, and the number of hybrid offspring from each successful cross.
Each breeding program should include a periodic, objective evaluation of the efficiency of the breeding procedure. Evaluation criteria vary depending on the goal and objectives, but should include gain from selection per year based on comparisons to an appropriate standard, overall value of the advanced breeding lines, and number of successful cultivars produced per unit of input (e.g., per year, per dollar expended, etc.).
Promising advanced breeding lines are thoroughly tested and compared to appropriate standards in environments representative of the commercial target area(s) for three years at least. The best lines are candidates for new commercial cultivars; those still deficient in a few traits are used as parents to produce new populations for further selection.
These processes, which lead to the final step of marketing and distribution, usually take from eight to 12 years from the time the first cross is made. Therefore, development of new cultivars is a time-consuming process that requires precise forward planning, efficient use of resources, and a minimum of changes in direction.
A most difficult task is the identification of individuals that are genetically superior, because for most traits the true genotypic value is masked by other confounding plant traits or environmental factors. One method of identifying a superior plant is to observe its performance relative to other experimental plants and to a widely grown standard cultivar. If a single observation is inconclusive, replicated observations provide a better estimate of its genetic worth.
The goal of plant breeding is to develop new, unique and superior squash inbred lines and hybrids. The breeder initially selects and crosses two or more parental lines, followed by repeated selfing and selection, producing many new genetic combinations. The breeder can theoretically generate billions of different genetic combinations via crossing, selfing and mutations. The breeder has no direct control at the cellular level. Therefore, two breeders will never develop the same line, or even very similar lines, having the same squash traits.
Each year, the plant breeder selects the germplasm to advance to the next generation. This germplasm is grown under unique and different geographical, climatic and soil conditions, and further selections are then made, during and at the end of the growing season. The inbred lines which are developed are unpredictable. This unpredictability is because the breeder's selection occurs in unique environments, with no control at the DNA level (using conventional breeding procedures), and with millions of different possible genetic combinations being generated. A breeder of ordinary skill in the art cannot predict the final resulting lines he develops, except possibly in a very gross and general fashion. The same breeder cannot produce the same line twice by using the exact same original parents and the same selection techniques. This unpredictability results in the expenditure of large research monies to develop a superior new squash inbred line.
The development of commercial squash hybrids requires the development of homozygous inbred lines, the crossing of these lines, and the evaluation of the crosses. Pedigree breeding and recurrent selection breeding methods are used to develop inbred lines from breeding populations. Breeding programs combine desirable traits from two or more inbred lines or various broad-based sources into breeding pools from which inbred lines are developed by selfing and selection of desired phenotypes. The new inbreds are crossed with other inbred lines and the hybrids from these crosses are evaluated to determine which have commercial potential.
Pedigree breeding is used commonly for the improvement of self-pollinating crops or inbred lines of cross-pollinating crops. Two parents which possess favorable, complementary traits are crossed to produce an F1. An F2 population is produced by selfing one or several F1's or by intercrossing two F1's (sib mating). Selection of the best individuals is usually begun in the F2 population; then, beginning in the F3, the best individuals in the best families are selected. Replicated testing of families, or hybrid combinations involving individuals of these families, often follows in the F4 generation to improve the effectiveness of selection for traits with low heritability. At an advanced stage of inbreeding (i.e., F6 and F7), the best lines or mixtures of phenotypically similar lines are tested for potential release as new cultivars.
Mass and recurrent selections can be used to improve populations of either self- or cross-pollinating crops. A genetically variable population of heterozygous individuals is either identified or created by intercrossing several different parents. The best plants are selected based on individual superiority, outstanding progeny, or excellent combining ability. The selected plants are intercrossed to produce a new population in which further cycles of selection are continued.
Backcross breeding has been used to transfer genes for a simply inherited, highly heritable trait into a desirable homozygous cultivar or inbred line which is the recurrent parent. The source of the trait to be transferred is called the donor parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent. After the initial cross, individuals possessing the phenotype of the donor parent are selected and repeatedly crossed (backcrossed) to the recurrent parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent.
Descriptions of other breeding methods that are commonly used for different traits and crops can be found in one of several reference books (e.g., “Principles of Plant Breeding” John Wiley and Son, pp. 115-161, 1960; Allard, 1960; Simmonds, 1979; Sneep et al., 1979; Fehr, 1987).
Proper testing should detect any major faults and establish the level of superiority or improvement over current cultivars. In addition to showing superior performance, there must be a demand for a new cultivar that is compatible with industry standards or which creates a new market. The introduction of a new cultivar will incur additional costs to the seed producer, the grower, processor and consumer; for special advertising and marketing, altered seed and commercial production practices, and new product utilization. The testing preceding release of a new cultivar should take into consideration research and development costs as well as technical superiority of the final cultivar. For seed-propagated cultivars, it must be feasible to produce seed easily and economically.
Once the inbreds that give the best hybrid performance have been identified, the hybrid seed can be reproduced indefinitely as long as the homogeneity of the inbred parent is maintained. A single-cross hybrid is produced when two inbred lines are crossed to produce the F1 progeny.
Squash is an important and valuable field crop. Thus, a continuing goal of plant breeders is to develop stable, high yielding squash hybrids that are agronomically sound. The reasons for this goal are obviously to maximize the amount of fruit produced on the land used as well as to improve the fruit agronomic qualities. To accomplish this goal, the squash breeder must select and develop squash plants that have the traits that result in superior parental lines for producing hybrids.